System and apparatus for recording and reproducing television video signals

ABSTRACT

The specification describes an improvement in multiple head, helical scan-type video, magnetic tape recorders. In greater detail, only one of two fields, which make each frame of the video signal, is recorded on a magnetic tape which travels at one half of the conventional running speed, the one field thus recorded is reproduced by both of the pair of magnetic heads, one after the other in succession, thereby reproducing a signal of one frame consisting of the two fields and constituting the original signal. 
     The system and apparatus for recording and reproducing television video signals according to this invention renders it possible to record and reproduce with substantially one half of the amount of the magnetic tape compared with that required for the conventional systems.

This application is a continuation-in-part of application Ser. No.340,379, filed Jan. 27, 1964 and now abandoned.

The present invention relates to a system and apparatus for recordingand reproducing television video signals, particularly to a system andapparatus which makes use of a video tape recorder provided with aplurality of magnetic heads wherein a magnetic tape is helically woundabout half the periphery of a rotary disc provided with at least a pairof magnetic heads, said magnetic tape is caused to travel in onedirection, and said rotary disk is caused to rotate so as to record thevideo signal on the magnetic tape with a sufficiently long loci inclinedon the magnetic tape in its lengthwise direction, and in which rendersit possible to record and reproduce with substantially one half of theamount of the magnetic tape compared with that required for theconventional systems.

Heretofore, methods have been proposed to decrease the amount of themagnetic tape required per unit television video signals at thesacrifice of the resolution of image in its transverse direction for thepurpose of increasing the density of records. In such conventionalmeans, however, sufficiently high density of records could not beobtained because it lowers the quality of the picture too much. It hasalso been proposed to increase the density of records still more, but atthe sacrifice of the resolution of the image in its longitudinaldirection. Such means, in general, has disadvantages in that itnecessitates a complex device for converting the television system.

In order to accomplish these objects the present invention provides asystem and apparatus for recording and reproducing television videosignals. The recorded television video signal comprises one frameconsisting of two fields, as in the conventional standard televisionvideo signals. However, only one of the two fields is recorded by one ofa pair of magnetic heads on a magnetic tape moving at one half of theconventional running speed. The alternate fields thus recorded arereproduced by both of the pair of magnetic heads, one after the other insuccession, thereby reproducing a signal of one frame consisting of thetwo fields and constituting the original signal.

The principal object of the present invention is to provide a system andapparatus for recording and reproducing television video signals, whichrenders it possible to record and reproduce television video signalswith substantially one half of the amount of magnetic tape per unitsignal, as compared with that required for the conventional system andapparatus for recording and reproducing television video signals.

Another object of the present invention is to provide a system andapparatus for recording and reproducing television video signals inwhich the amount of signal information to be recorded is reduced by onehalf, which results in a decrease of the necessary amount of themagnetic tape to about one half that required by the conventionalsystem, and which is suitable for applying to a small type video taperecorder for use in industry or household etc. where there is no needfor a completely accurate image resolution.

A further object to provide a system and apparatus for recording andreproducing television video signals, which permits simultaneouslymonitoring the recorded signal and still attaining the above mentionedobject.

For a better understanding of the present invention, reference is madeto the accompanying drawings, in which:

FIG. 1 shows diagrammatically a plan view of the relative arrangement ofone embodiment of a video tape recorder provided with two magnetic headsfor which the invention is applied;

FIG. 2 is an enlarged section of line A-B of a guide drum of the videotape recorder shown in FIG. 1;

FIG. 3 is a perspective view of the guide drum shown in FIG. 2 wound bya magnetic tape;

FIG. 4 is an enlarged view of a part of the magnetic tape showing tracksrecorded thereon by means of magnetic heads according to the invention;

FIG. 5 is an enlarged view of a part of the magnetic tape showing tracksrecorded thereon by means of magnetic heads of the conventionalapparatus;

FIG. 6 shows diagrammatically a plan view of the relative arrangement ofthe other embodiment of a rotary disk having magnetic heads for use inthe present invention; and

FIG. 7 shows a sectional side view of the rotary disk shown in FIG. 6.

In FIG. 1, a magnetic tape supply reel 1 is arranged on a plane which isvertically higher than a take up reel 2. A magnetic tape 3, deliveredfrom the supply reel 1, is fed via a flanged roller 5 having a tensionarm 4 and a magnetic erasing head 6 erases any signal which waspreviously recorded on the tape over the whole width thereof during therecording operation. The tape is brought to a guide drum 9 enclosingtherein a rotary disk 19, to be described hereinafter. The magnetic tape3 is wound around the guide drum 9 for half the periphery in the shapeof Ω by the aid of guide rollers 7 and 8. The magnetic tape 3 is thenbrought into contact with a stationary magnetic head 10 for recording anaudio signal, control signal etc. and fed via a capstan 11, a pinchroller 12, adapted to press the tape 3 against the capstan 11, and aflanged roller 13 having a tension arm 14 to the take up reel 2 wherethe tape 3 is wound around it. Further, the capstan 11 causes the tapeto travel at a predetermined speed slower than that in the conventionalapparatus, as described later.

FIG. 2 shows an enlarged sectional view taken on line A-B of the guidedrum 9 shown in FIG. 1. In FIG. 2, an upper guide drum 15 is enclosed bya cover 15' and a lower guide drum 16 is arranged coaxially with theupper guide drum 15. The upper and lower guide drums 15 and 16 aresupported by a supporting plate 17 so as to form a suitable gap 18therebetween. A rotary disk 19 has, at its periphery, a pair of magneticheads 20 and 21 arranged diametrically opposite one another. The rotarydisk 19 is secured to a rotary shaft 22 so as to be rotated in the gapformed between the upper and lower guide drums 15 and 16. The magneticheads 20 and 21 are secured to the rotary disk 19 so that these magneticheads are located at different heights in a stepwise manner to bedescribed hereinafter. A rotary shaft 23 of a motor 24 is fitted in thelower part of the rotating shaft 22 and secured thereto by means of aset screw 25. A bearing cartridge 26 comprises an upper bearing unit 27and a lower bearing unit 28. A carrier plate 29 is used for supportingthe above mentioned members.

The magnetic tape 3 is helically wound around the guide drum 9 forsubstantially half the periphery in a manner such that the longitudinalaxis of the magnetic tape is inclined with respect to the rotating planeof the magnetic heads 20 and 21.

Next to be described is the recording operation of the inventiveapparatus.

The magnetic tape 3 is wound around the guide drum for half theperiphery in the shape of Ω as shown in FIG. 3. The rotating speed ofthe rotary disk 19 is made considerably greater than the peripheralspeed of the magnetic tape 3 in order to record the signal on the tape 3by means of the magnetic heads. Thus, there is recorded on the magnetictape tracks having a sufficiently long loci and being inclined at anangle of θ on the magnetic tape with respect to its longitudinaldirection, as shown in FIG. 4 wherein each track includes the signalscorresponding to one field.

If a video signal current is supplied to one of the magnetic heads 20 or21, for example, to the magnetic head 20, and one frame of the videosignal current consists of even and odd fields, then the one trackrecorded on the magnetic tape 3 consists of only one field signal. Theother field of the same frame is not recorded on the magnetic tape. Onefield signal of the next frame is then recorded on the adjacent track.Accordingly, each of thus recorded tracks is formed by only one or theother of even and odd fields. At this time, the gap between each trackcan be made similar to that in the conventional system by determiningthe running speed of the magnetic tape to a predetermined speed of onehalf that required by the conventional system. Contrary to the above, inby the conventional apparatus each frame shown by I, II, III . . . etc.,as shown in FIG. 5 consists of two tracks, each forming one field. Inaccordance with the system and apparatus according to the presentinvention, each frame shown by I, II, III . . . etc., in FIG. 4 consistsof only one track, which results in a decrease of the necessary amountof the magnetic tape by one half that required by the conventionalsystem.

Moreover, one of the pair of magnetic heads 20 or 21, that is, themagnetic head 21, which was not used in the exemplary recordingoperation, is mounted on the rotary disk 19 in a stepwise manner withrespect to the magnetic head 20 so that the magnetic head 21 scans thesame track recorded by the magnetic track 20. Thus, the inventionenables the magnetic head 21 to be used, as a monitor head in therecording operation though the head reproduces only one field in aframe.

A reproducing operation of the invention will now be explained.

In case of reproducing the recorded signal, both of the magnetic heads20 and 21 are caused to be operated. During one half period of onerotation of the rotary disk 19, the magnetic head 20 scans one of therecorded tracks such, for example, as the recorded track I in FIG. 4 toreproduce one field. During another one half period of the same onerotation of the rotary disk 19, the magnetic head 21 comes into contactwith the magnetic tape 3 and scans the same track I to reproduce thesame one field. The fields thus reproduced by the magnetic heads 20 and21, respectively, are added together to reproduce one frame signalconsisting of two fields similar to the original signal. During next onerotation of the rotary disk 19, the two heads 20 and 21 scan the nextadjacent track II in FIG. 4, one after the other in succession to effectthe reproducing operation. Thus, a continuous image picture can bereproduced.

Next, FIGS. 6 and 7 show the other embodiment of a rotary disk havingmagnetic heads for use in the present invention. A magnetic recordingand reproducing head 30 records only one of even or odd fields on eachtrack of the magnetic tape 3 in the recording operation, and reproducesthe signal recorded on said track in the reproducing operation, as likeas the magnetic head 20 in the first embodiment. A magnetic reproducinghead 31 is mounted at a position where a distance D apart in ahorizontal direction and a height H different in a vertical directionfrom the position diametrically opposite to said magnetic head 30 at theperipheral edge of the rotary disk 19, and is used only for reproducingsaid recorded track. If the magnetic tape running speed is determined asV, the frame numbers of the video signal every second as X, the angle ofthe recording track on the tape to the tape edge as θ and the lengthcorresponding to a horizontal scanning period in the recording track onthe tape as L, the following equations are given: ##EQU1## Assume thatthe magnetic reproducing head 31 is on a plane which is lower, by thedistance H, than the mounting plane of the magnetic recording andreproducing head 30. The magnetic reproducing head 31 is then mounted ata position on the circumference of disk 19 which is offset (in acounterclockwise direction), by the distance D, from a diameter of thedisk 19 which runs through the magnetic head 30. This is shown in FIG.6. Conversely, if the head 31 is higher than the head 30, the offsetdistance D is in a clockwise direction. Or if the direction of tapetravel is reversed, the offset directions are also reversed.

If the magnetic head 31 is mounted as described above, the portion, inwhich a field signal reproduced by said magnetic head 30 and a fieldsignal reproduced by said magnetic head 31 overlap each other, can bemade to minimum when the signals reproduced by said both heads arecomposed, and the signalless portion can be made to minimum. And furthersaid magnetic head 31 can trace the same scanning track following saidmagnetic head 30, as described in the above embodiment. In said equation##EQU2## is the term for which the signal recorded as even or oddfields, is reproduced as odd or even fields in interlaced relation. Forexample, if the value of ##EQU3## the value of D becomes 3L or 4L, andif the recorded signal consists of odd fields, the odd fields arereproduced by the magnetic head 30, and in succession the signal tracesof these odd fields are reproduced as even fields by the magnetic head31, thereby each frame signal comprising two fields which renders itpossible to interlace, can be reproduced.

Further, in this embodiment the switching positions of the reproducingsignals by the magnetic heads 30 and 31 are selected before and after avertical synchronizing signal which is in front or rear of each fieldvideo signal reproduced by the magnetic head 30. That is, a signalreproduced by the magnetic head 30 is used as the vertical synchronizingsignal usually and is composed with a video signal out of a signalreproduced by the magnetic head 31.

Furthermore, the present invention can prevent from producing asignalless portion at the beginning of each field reproduced by saidmagnetic head 31 by winding the tape 3 over more than half portion ofthe periphery of the guide drum 9 so that each track includes more thanone field signals, in said first embodiment without spacing saidmagnetic head 31 by D.

What I claim is: .[.1. A system for recording and playing back a videosignal comprising a rotary body, means for mounting a magnetic recordingand reproducing head and a magnetic reproducing head on the periphery ofsaid rotary body, a magnetic recording medium, means for moving saidrecording medium past said rotary body at a predetermined speed forrecording said video signal in parallel oblique tracks on said medium,means for rotating said rotary body with a velocity relative to saidspeed such that a video signal of one field is recorded in one track onsaid medium, means for applying said video signal of alternate fields tosaid magnetic recording and reproducing head, no video signal beingapplied to said magnetic reproducing head during a recording process,means for locating said reproducing head at a position on said rotarybody wherein said reproducing head traces the track recorded by saidrecording and reproducing head with a time lag of one field period, afirst means comprising said recording and reproducing head for playingback said video signal of alternate fields, a second means comprisingsaid reproducing head for playing back said video signal of alternatefields with a time lag of one field period, and means for sequentiallyinterlacing the signal reproduced by said first means with the signalreproduced by said second means..].
 2. A system for recording andplaying back a video signal .[.as defined in claim 1 and.]..Iadd.comprising a rotary body; means for mounting a magnetic recordingand reproducing head and a magnetic reproducing head on the periphery ofsaid rotary body; a magnetic recording medium; means for moving saidrecording medium past said rotary body at a predetermined speed forrecording said video signal in parallel oblique tracks on said medium;means for rotating said rotary body with a velocity relative to saidspeed such that a video signal of one field is recorded in one track onsaid medium; means for applying said video signal of alternate fields tosaid magnetic recording and reproducing head; means for locating saidreproducing head at a position on said rotary body wherein saidreproducing head traces the track recorded by said recording andreproducing head with a time lag of one field period; .Iaddend.meanscomprising said reproducing head for playing back said video signal ofalternate fields during the recording process, said playback being for amonitoring use.Iadd.; a first means comprising said recording andreproducing head for playing back said video signal of alternate fieldsduring the reproducing process; a second means comprising saidreproducing head for playing back said video signal of alternate fieldswith a time lag of one field period during the reproducing process; andmeans for sequentially interlacing the signal reproduced by said firstmeans with the signal reproduced by said second means.Iaddend.. .[.3. Asystem for recording and playing back a video signal as defined in claim1 wherein said reproducing head is mounted at a position on theperipheral edge of said rotary body in a plane which is parallel to theplane in which the recording and reproducing head is mounted..]. .[.4. Asystem for recording and playing back a video signal as defined in claim1 in which said reproducing head is mounted in a rotating plane and at aposition on the peripheral edge of said rotary body which is apredetermined distance apart from the position of a rotating plane inwhich said recording and reproducing head is mounted, said reproducinghead being another distance apart from a position diametrically oppositeto said recording and reproducing head so that there is a minimumoverlap of the video signal reproduced by said recording and reproducinghead and the video signal reproduced by said reproducing head..].
 5. Asystem for recording and playing back a video signal .[.as defined inclaim 1 wherein said first means includes.]. .Iadd.comprising a rotarybody; means for mounting a magnetic recording and reproducing head and amagnetic reproducing head on the periphery of said rotary body; amagnetic recording medium; means for moving said recording medium pastsaid rotary body at a predetermined speed for recording said videosignal in parallel oblique tracks on said medium; means for rotatingsaid rotary body with a velocity relative to said speed such that avideo signal of one field is recorded in one track on said medium; meansfor applying said video signal of alternate fields to said magneticrecording and reproducing head, no video signal being applied to saidmagnetic reproducing head during a recording process; means for locatingsaid reproducing head at a position on said rotary body wherein saidreproducing head traces the track recorded by said recording andreproducing head with a time lag of one field period; a first meanscomprising .Iaddend.said recording and reproducing head for playing backthe video signal of alternate fields having vertical synchronizingsignals in front and in rear thereof .[.and said.]..Iadd.; a.Iaddend.second means .[.comprises.]. .Iadd.comprising .Iaddend.saidreproducing head for reproducing .Iadd.with a time lag of one fieldperiod .Iaddend.said video signal of alternate fields in which saidvertical synchronizing signals are removed.Iadd.; and means forsequentially interlacing the signal reproduced by said first means withthe signal reproduced by said second means.Iaddend..
 6. An apparatus forrecording and reproducing television video signals comprising a rotarybody provided on opposite sides of its periphery with a magneticrecording and reproducing head and a magnetic reproducing head, amagnetic medium, means for moving said medium past said rotary body at apredetermined speed, means comprising at least one of said heads forrecording said video signal in parallel oblique tracks on said magneticmedium, means for rotating said rotary body with a velocity in which avideo signal of one field is recorded in one track on said magneticmedium, means for applying said video signal of alternate fields to saidmagnetic recording and reproducing head, no video signal being appliedto said magnetic reproducing head during a recording term, means formounting said reproducing head at a position on the peripheral edge ofsaid rotary body which is a distance D away from the diameter in arotating plane of said recording and reproducing head and at a positionwhich is a distance H apart in a vertical direction from said rotatingplane, a first means for reproducing said video signal of alternatefields by said recording and reproducing head, a second means forreproducing said video signal of alternate fields with a time lag of onefield period by said reproducing head during reproducing time, and meansfor sequentially interlacing the signal reproduced by said first meanswith the signal reproduced by said second means, wherein ##EQU4## Vindicates a magnetic tape speed, X numbers of the frame of a videosignal per every second, θ angle of the recorded track on said magneticmedium to the edge of said magnetic medium, and L length of the trackcorresponding to a horizontal scanning period.